The fact that the aircraft remained upright and floating in daylight conditions contributed to the successful evacuation of the cabin without injury and enabled about half of the passengers to locate and don their life vests. Power loss of the No2engine was a consequence of the installation of the planetary gear oil strainer at overhaul. This is believed to have been a sporadic occurrence, however, PWC has recognized possible installation problems of the strainer. As such, the applicable Overhaul Manual was revised in 1998 to clarify the installation procedure of the strainer screen. The subject engine was overhauled in 1993 prior to the change in the manuals. Even though fractures in the planet gear oil strainer screen are not believed to have been a recent or sudden event, an unsafe condition existed. The West Coast Air maintenance procedure in effect prior to the accident exceeded the requirements of the de Havilland EMMA program. In spite of additional precautions, an unsafe condition developed during the unmonitored period between inspections. Regulations require the installation of engine oil chip detectors, but do not require the associated annunciator system on the DHC-6. Without an annunciator system, monitoring of engine oil contamination is limited to the frequency and thoroughness of maintenance inspections. An annunciator system would have provided a method of continuous monitoring and may have warned the crew of the impending problem. Take-off is the most critical time for a power loss, and the response procedure can vary from simple to complex. The flight crew must take immediate action to maintain control of the aircraft and decide, based on a number of critical factors, whether to force land or to climb away from the point of the power loss. Considerable handling skills are required to overcome an unexpected loss of power in a twin-engine aircraft shortly after take-off, while at low altitude. However, the first and highest priority is to maintain control of the aircraft. With the aircraft just reaching 70KIAS when the power loss occurred, an immediate and aggressive control input to lower the nose would be required to prevent deceleration to Vmc or below. Below Vmc, maintaining control of the aircraft (with the remaining engine at take-off power) becomes impossible due to the inability of the rudder to overcome the asymmetric thrust condition. The selection of full flaps decreased the stall speed from 60 to 55KIAS, but it also significantly increased the aerodynamic drag. The drag from the flaps and the windmilling propeller resulted in a continuing loss of airspeed and a progressive loss of rudder authority due to asymmetric thrust. The AFM-recommended emergency procedure for rejecting a take-off due to a power loss while airborne and below Vmc is to reduce power on the operating engine, sufficiently to assure control of the airplane, and land straight ahead. The airspeed was above Vmc at the time of the power loss and the crew agreed to reject the take-off and land straight ahead. The airspeed was subsequently allowed to fall below Vmc, possibly due to the increasing drag of the extending flaps and the crew's distraction with fire fighting rather than focusing upon maintaining control and landing. When the airspeed fell below Vmc, any incremental reduction in power on the operating engine would have contributed to increased control as long as the airspeed did not decrease further. The power on the remaining engine was not reduced until impact was imminent.Analysis The fact that the aircraft remained upright and floating in daylight conditions contributed to the successful evacuation of the cabin without injury and enabled about half of the passengers to locate and don their life vests. Power loss of the No2engine was a consequence of the installation of the planetary gear oil strainer at overhaul. This is believed to have been a sporadic occurrence, however, PWC has recognized possible installation problems of the strainer. As such, the applicable Overhaul Manual was revised in 1998 to clarify the installation procedure of the strainer screen. The subject engine was overhauled in 1993 prior to the change in the manuals. Even though fractures in the planet gear oil strainer screen are not believed to have been a recent or sudden event, an unsafe condition existed. The West Coast Air maintenance procedure in effect prior to the accident exceeded the requirements of the de Havilland EMMA program. In spite of additional precautions, an unsafe condition developed during the unmonitored period between inspections. Regulations require the installation of engine oil chip detectors, but do not require the associated annunciator system on the DHC-6. Without an annunciator system, monitoring of engine oil contamination is limited to the frequency and thoroughness of maintenance inspections. An annunciator system would have provided a method of continuous monitoring and may have warned the crew of the impending problem. Take-off is the most critical time for a power loss, and the response procedure can vary from simple to complex. The flight crew must take immediate action to maintain control of the aircraft and decide, based on a number of critical factors, whether to force land or to climb away from the point of the power loss. Considerable handling skills are required to overcome an unexpected loss of power in a twin-engine aircraft shortly after take-off, while at low altitude. However, the first and highest priority is to maintain control of the aircraft. With the aircraft just reaching 70KIAS when the power loss occurred, an immediate and aggressive control input to lower the nose would be required to prevent deceleration to Vmc or below. Below Vmc, maintaining control of the aircraft (with the remaining engine at take-off power) becomes impossible due to the inability of the rudder to overcome the asymmetric thrust condition. The selection of full flaps decreased the stall speed from 60 to 55KIAS, but it also significantly increased the aerodynamic drag. The drag from the flaps and the windmilling propeller resulted in a continuing loss of airspeed and a progressive loss of rudder authority due to asymmetric thrust. The AFM-recommended emergency procedure for rejecting a take-off due to a power loss while airborne and below Vmc is to reduce power on the operating engine, sufficiently to assure control of the airplane, and land straight ahead. The airspeed was above Vmc at the time of the power loss and the crew agreed to reject the take-off and land straight ahead. The airspeed was subsequently allowed to fall below Vmc, possibly due to the increasing drag of the extending flaps and the crew's distraction with fire fighting rather than focusing upon maintaining control and landing. When the airspeed fell below Vmc, any incremental reduction in power on the operating engine would have contributed to increased control as long as the airspeed did not decrease further. The power on the remaining engine was not reduced until impact was imminent. A planetary gear disintegrated in the propeller reduction gearbox of the No2engine and caused the engine drive shaft to disconnect from the propeller, resulting in a loss of propulsion from this engine. The planetary gear oil strainer screen wires fractured by fatigue as a consequence of the installation at the last overhaul. This created an unsafe condition and it is most probable that the release of wire fragments and debris from this strainer screen subsequently initiated or contributed to distress of the planetary gear bearing sleeve and resulted in the disintegration of the planetary gear. Although airspeed was above Vmc at the time of the power loss, the aircraft became progressively uncontrollable due to power on the remaining engine not being reduced to relieve the asymmetric thrust condition until impact was imminent.Findings as to Causes and Contributing Factors A planetary gear disintegrated in the propeller reduction gearbox of the No2engine and caused the engine drive shaft to disconnect from the propeller, resulting in a loss of propulsion from this engine. The planetary gear oil strainer screen wires fractured by fatigue as a consequence of the installation at the last overhaul. This created an unsafe condition and it is most probable that the release of wire fragments and debris from this strainer screen subsequently initiated or contributed to distress of the planetary gear bearing sleeve and resulted in the disintegration of the planetary gear. Although airspeed was above Vmc at the time of the power loss, the aircraft became progressively uncontrollable due to power on the remaining engine not being reduced to relieve the asymmetric thrust condition until impact was imminent. The propeller reduction gearboxes were inspected in accordance with the West Coast Air maintenance control manual. These inspections exceeded requirements of the de Havilland Equalized Maintenance Maximum Availability program. Since the last inspection, 46 hours of flight time before the accident, did not reveal any anomaly, a risk remains of adverse developments with resulting consequences occurring during the unmonitored period between inspections. Regulations require the installation of engine oil chip detectors, but not the associated annunciator system on the DHC-6. Without an annunciator system, monitoring of engine oil contamination is limited to the frequency and thoroughness of maintenance inspections. An annunciator system would have provided a method of continuous monitoring and may have warned the crew of the impending problem. Although regulations do not require the aircraft to be equipped with an auto-feather system, its presence may have assisted the flight crew in handling the sudden loss of power by reducing the drag created by a windmilling propeller. Since most air taxi and commuter operators use their own aircraft rather than a simulator for pilot proficiency training, higher-risk emergency scenarios can only be practiced at altitude and discussed in the classroom. As a result, pilots do not gain the benefit of a realistic experience during training.Findings as to Risk The propeller reduction gearboxes were inspected in accordance with the West Coast Air maintenance control manual. These inspections exceeded requirements of the de Havilland Equalized Maintenance Maximum Availability program. Since the last inspection, 46 hours of flight time before the accident, did not reveal any anomaly, a risk remains of adverse developments with resulting consequences occurring during the unmonitored period between inspections. Regulations require the installation of engine oil chip detectors, but not the associated annunciator system on the DHC-6. Without an annunciator system, monitoring of engine oil contamination is limited to the frequency and thoroughness of maintenance inspections. An annunciator system would have provided a method of continuous monitoring and may have warned the crew of the impending problem. Although regulations do not require the aircraft to be equipped with an auto-feather system, its presence may have assisted the flight crew in handling the sudden loss of power by reducing the drag created by a windmilling propeller. Since most air taxi and commuter operators use their own aircraft rather than a simulator for pilot proficiency training, higher-risk emergency scenarios can only be practiced at altitude and discussed in the classroom. As a result, pilots do not gain the benefit of a realistic experience during training. The fact that the aircraft remained upright and floating in daylight conditions contributed to the successful evacuation of the cabin without injury and enabled about half of the passengers to locate and don their life vests. The aircraft was at low altitude and low airspeed at the time of power loss. The selection of full flaps may have contributed to a single-engine, high-drag situation, making a successful landing difficult.Other Findings The fact that the aircraft remained upright and floating in daylight conditions contributed to the successful evacuation of the cabin without injury and enabled about half of the passengers to locate and don their life vests. The aircraft was at low altitude and low airspeed at the time of power loss. The selection of full flaps may have contributed to a single-engine, high-drag situation, making a successful landing difficult. Since this accident, the operator has revised its pilot emergency training syllabus. The revised syllabus, approved by Transport Canada, places increased emphasis on aircraft handling and emergency procedures in response to loss of power at low altitude and low airspeed. The operator's revision goes beyond the minimum standards required by Transport Canada. The operator has also revised its maintenance inspection program. The weekly airframe and engine inspection (AE) now incorporates an electrical continuity test of the engine oil chip detector on the propeller reduction gearbox casing. Pratt Whitney Canada has confirmed that the Overhaul Manual applicable to the PWC PT6-20 series engine RGB was revised in 1998 to clarify the installation procedure of the planetary gear oil strainer screens.Safety Action Taken Since this accident, the operator has revised its pilot emergency training syllabus. The revised syllabus, approved by Transport Canada, places increased emphasis on aircraft handling and emergency procedures in response to loss of power at low altitude and low airspeed. The operator's revision goes beyond the minimum standards required by Transport Canada. The operator has also revised its maintenance inspection program. The weekly airframe and engine inspection (AE) now incorporates an electrical continuity test of the engine oil chip detector on the propeller reduction gearbox casing. Pratt Whitney Canada has confirmed that the Overhaul Manual applicable to the PWC PT6-20 series engine RGB was revised in 1998 to clarify the installation procedure of the planetary gear oil strainer screens.